This research proposal is designed to evaluate the early transcriptional modulations during steroid induction in the rat uterus. It will examine the possible equilibrium between associated (engaged) RNA polymerases and dissociated (free) RNA polymerases. In individual RNA polymerases will be analysed on the basis of their isoelectric point and classified according to their sensitivity to an amanitin. An evaluaton of the temporal sequence of event will be made to correlate (a) hormone receptor binding to chromatin, (b) immediate changes in individual RNA polymerases either by a dissociation from the engaged to the free form or by an association from the free to the engaged form, and (c) immediate changes in DNA template availability. The major methodology in this proposal is to adapt a method of isoelectric focussing already proven to be valuable in RNA polymerase fractionation in a soybean seedling system to the rat uterus system.